Astronomik 6 nm S-II MFR Narrowband Emission-line Filter
Canon EOS Full Format XL Clip.
Astronomik SII Narrowband Filters are suitable for false color imaging of emission nebulae emanating singly ionized sulfur. The contrast between an object glowing at 672 nm and the background is increased significantly due to the high transmission and effective out-of-band blocking!
The SII line (672 nm) is in the deep red portion of the spectrum, beyond H-alpha.
This Astronomik SII MFR Narrowband filter has a 6 nm FWHM (Full Width at Half Maximum) coating. The extra narrow bandpass of 6 nm filters are most appreciated with cameras that offer extremely low dark current and good cooling, or when imaging in areas with severe light pollution. The higher level of out-of-band blocking allows you to take longer exposures and choose objects embedded in normally over-bright, crowded areas of the Milky Way. Extra blocking causes faint stars to disappear from the background, and brighter stars will be pin-pricks of light.
Images: The EOS XL clip image is shown for the clip with a different filter/color. This filter has the same filter as seen in the image of a 1.25-inch filter. Your filter will be the "red glass" in an EOS Full Format XL Clip.
Astronomik MFR Narrowband Emission Line Filter Highlights
Special Coatings Allow Filter Use Across Most Focal Ratios: Astronomik Narrowband Emission-line filters have been designed to be used with a wide range of focal ratios. The special MFR (multi-focal ratio) coatings applied to the 12 nm FWHM filters make them compatible with optics as fast as f/3, and the 6 nm models perform well with focal ratios as fast as f/4. This means you won't need to buy different filters for your fast refractor and your SCT, and you won't have to pay premium prices for high-speed filters.
Amazingly High Out of Band Blocking: Astronomik Narrowband Emission-line Filters offer superb blocking of unwanted wavelengths, from UV up to IR. Transmission of 90-percent is guaranteed by Astronomik, but the typical transmission can be as high as 96-percent on both 6 nm and 12 nm Narrowband filters. This feature translates to extremely high contrast and pleasingly dark background skies, even under heavily light-polluted conditions, allowing you to take longer exposures if you so desire without creating an overly bright (or saturated) background. Another benefit of good out-of-band blocking is the reduction of stray light and halos. Stars display as sharp points of light on a velvety black background, providing the perfect backdrop for the deep-sky object you are imaging.
Image During Full Moon or Under Light Polluted Skies: Because Astronomik Narrowband Emission Line Filters have a high transmission rate for the chosen wavelength but blocks pretty much everything else, you can image from your own backyard, even if your neighborhood suffers from light-pollution (which is pretty much everybody). If it is a beautiful night with great seeing but the Moon phase doesn't support visual deep-sky astronomy, you can pull out your telescope, camera, and Astronomik filters and still get great results.
Ten Year Warranty! Astronomik filters will last for many years without degradation of the coatings, due to the quality of the substrate and coatings used. The high-quality glass is optically polished and is free of stress and striae. The coatings used on Astronomik filters are applied in multiple layers, making the resulting filter scratch resistant and unaffected by moisture or aging that some filters of less quality may be prone to. Astronomik filters are also parfocal due to the small thickness tolerance allowed. Astronomik backs up this quality with a ten-year warranty.
- The horizontal axis is the Wavelength in Nanometers (nm). 400 nm is deep blue, at 520 nm the human eye senses green and at 600 nm red. At 656 nm is the famous "H-Alpha" emission line of hydrogen.
- The transmission in % is plotted on the vertical axis.
- The red line shows the transmission of the filter.
Visual filters: The grey line in the background shows the relative sensitivity of the human eye at night. The maximum is at approximately 510 nm and drops to longer and shorter wavelengths. You can easily see, that you can't see anything of the H-alpha line at night (even if you can during daylight!) The sensitivity at 656 nm is 0% at night!
Photographic filters: The grey line in the background shows the sensitivity of a typical CCD sensor.
- The most important artificial emission lines are shown in orange. The artificial light pollution is dominated by see mercury (Hg) and sodium (Na), which are used in nearly all streetlights.
- The most important emission lines from nebulas are shown in green. The most important lines are from ionized Hydrogen (H-alpha and H-beta) and double ionized oxygen (OIII).
The major emission lines of artificial light pollution:
| Hg 435.8 nm | Hg 546.1 nm | Hg 577.0 nm | Hg 578.1 nm |
| Na 589.0 nm | Na 589.6 nm | Na 615.4 nm | Na 616.1 nm |
The major emission lines of nebulas:
H-β 486.1 nm | OIII 495.9 nm | OIII 500,7 nm | H-α 656.3 nm
- Compatible cameras:
- 5D Mk I (no live view)
- 5D Mk II
- 5D Mk III
- 6D Mk I
- Non-compatible cameras:
- 5D Mk IV
- 6D Mk II
- Canon APS-C (EF-S) cameras
- Canon Mirrorless cameras